Sheet flattening method

Abstract

A method and apparatus for flattening curled ones of a plurality of moving paper sheets subsequent to the printing and at least partial drying thereof is disclosed. The sheets are transported sequentially along a transport path, and the selected sheets are heated to a plasticizing temperature. The selected sheets are then stretched in both a longitudinal and a lateral direction with respect to the transport direction of the sheets.

What is claimed is: 
     
       1. A method for operating upon selected ones of a plurality of moving paper sheets for flattening of the selected sheets subsequent to the printing thereon with a liquid ink, comprising the steps of: transporting the sheets sequentially along a transport path;   heating the selected sheets during transportation thereof along said transport path;   applying a stretching force to the selected sheets in a longitudinal direction with respect to the sheets during transportation thereof along said transport path; and   applying a stretching force to the selected sheets in a   lateral direction with respect to the sheets during transportation thereof along said transport path;   said heating of the selected sheets being performed at a first predetermined location along said transport path;   said heating of the selected sheets further being performed by a heater selectively movable between a first position remote from said transport path and a second position adjacent said first predetermined location and said transport path, and wherein said heating step includes: moving said heater from said first position to said second position prior to transporation of a selected sheet past said first predetermined location;   in the event the next succeeding sheet of the moving sheets is a selected sheet, retaining said heater in said second position; and   in the event the next succeeding sheet of the moving sheets is not a selected sheet, moving said heater from said second position to said first position.     
     
     
       2. A method for operating upon selected ones of a plurality of moving paper sheets for flattening of the selected sheets subsequent to the printing thereon with a liquid ink, comprising the steps of: transporting the sheets sequentially along a transport path;   heating the selected sheets during transportation thereof along said transport path;   applying a stretching force to the selected sheets in a longitudinal direction with respect to the sheets during transportation thereof along said transport path; and   applying a stretching force to the selected sheets in a lateral direction with respect to the sheets during transportation thereof along said transport path;   said heating of the selected sheets being performed at a first predetermined location along said transport path;   said application of said longitudinal stretching force and said lateral stretching force being performed on the selected sheets simultaneously and at a second predetermined location along said transport path;   said application of said lateral stretching force to the selected sheets being performed by: applying compressive force to the selected sheets at said second predetermined location along said transport path, and   converting said compressive force to said lateral stretching force;     said application of said compressive force to selected sheets being performed by a pair of oppositely-driven rollers disposed in selectively compressive mutual contact for movement of sheets therebetween along said transport path;   said application of said compressive force to selected sheets including: mutually compressing said rollers to produce said compressive force therebetween prior to transportation of a selected sheet past said second predetermined location;   in the event the next succeeding sheet of the moving sheets is a selected sheet, maintaining said rollers in compression to produce said compressive force; and   in the event the next succeeding sheet of the moving sheets is not a selected sheet, relieving compression between said rollers at least partially to produce at least substantially less than said compressive force between said rollers.